分析电火花表面强化层的应力场特点,建立三维应力场模型,并利用APDL编程实现对应力场的有限元数值模拟,给出强化层和基体在不同位置、不同方向的应力分布和变化规律.结果表明:强化过程中,熔池及附近区域存在的巨大且剧烈变化的温度梯度和不一致的冷却速率使试样产生很大的热应力;由于热导率和热膨胀系数存在差异的缘故,各节点的应力值随着位置的变化而变化;试样的应力曲线在热影响区都存在突变,有强化层时,由于强化层和基体材料的比热容C和热导率,κ不一致,加剧应力曲线在热影响区的突变;采用梯度强化层和热处理工艺可以有效地改善电火花表面强化层的应力分布.
The characteristic of stress field for electrical discharge strengthening coating was analyzed. A model of 3D stress field was proposed. The 3D numerical simulation analysis for electrical discharge strengthening was conducted with the ANSYS parametric design language (APDL). The distribution of stress was given at different fixed point and different directions for coating and substrate. During the strengthening, in melting bath and adjacent area, the stress formation is due to the giant and variable temperature gradient and the different cooling velocity. Because there exists difference in the heat conductivity and the coefficient of thermal expansion at different position and along different direction in the material, the value of stress is varying with the position and direction. The distribution of stress abruptly changes at heat-affected area, and for strengthened coating, because there exists difference in c and κ in strengthened coating and the matrix material, the varying of the stress is aggravated. Experiment results indicated that gradient coating and heat treatment can improve the distribution of thermal stress in strengthened coating.
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